$\dfrac{9}{4} \div \dfrac{1}{9} = {?}$
Explanation: Dividing by a fraction is the same as multiplying by the reciprocal of the fraction. The reciprocal of $\dfrac{1}{9}$ is $\dfrac{9}{1}$ Therefore: $ \dfrac{9}{4} \div \dfrac{1}{9} = \dfrac{9}{4} \times \dfrac{9}{1} $ $ \phantom{\dfrac{9}{4} \times \dfrac{9}{1}} = \dfrac{9 \times 9}{4 \times 1} $ $ \phantom{\dfrac{9}{4} \times \dfrac{9}{1}} = \dfrac{81}{4} $